Restoration of faded ink writings



United States Patent RESTORATION OF FADED INK WRITINGS Lloyd H. .Almy, Pittsburgh, Pa., assignor to Carl E. Hultman, Pittsburgh, Pa.

No Drawing. Application July .22, 1957 Serial No. 673,135

Claims. (Cl. 8-7) This invention relates to a method of restoring faded writing made with iron inks, and this application is a continuation-in-part of my copending application Serial No. 424,249, filed April 19, 1954.

It is well known that writings made with iron inks such, for example, as iron-tannin inks, fade with the passage of time due presumably, to oxidation of the iron of the ink to ferric oxide (Fe O Patent No. 2,182,672 describes and claims a method of restoring such faded writings in accordance with which the paper bearing the writing is treated with an acidified aqueous solution of an alkali metal halide, e. g., sodium-chloride (NaCl), and potassium ferrocyanide [K Fe(CN) after which the paper is washed and then subjected to the action of a solution of a compound, such as zinc chloride (ZnCl to precipitate residual potassium ferrocyanide as an insoluble and stable substance of color contrasting to that of the revived ink characters, after which the paper is again washed and then dried.

The method of that patent has been used extensively over the years, butalthough it does act to'restore the ink characters successfully, experience has shown thatat times the restored characters show edge blurring, Wherefore the appearance is impaired. Although the exact reason for such blurring is not known definitely, it may be due to migration of the Prussian blue formed by the treatment with alkalimetal ferrocyanide, or it may be due to the formation of a slightly soluble modification of Prussian blue,.or to other factors.

It is among the objects of this invention to provide an improvedmethod of restoring faded iron ink writings with an acidic aqueous solution of a soluble alkali metal ferrocyanide and an alkali metal halide that satisfactorily restores the brilliance and legibility of the ink characters while suppressing edge blurring, that dispenses with the precipitating step of the aforesaid patented method, and that is rapid and easilyperformed.

A furtherobject is ,to restore without edge blurring faded iron ink writings by means of aqueous acidic calcium or barium ferrocyanide, in which the use of alkali metal halide is not needed. 1

Other objects will berecognized from the following specification.

The invention is predicated in part upon my discovery that in the use of solutions containing an alkali metal ferrocyanide, an acid, and an alkali metal halide for ink restoring, edge blurring of the characters is suppressed satisfactorily by including in the solution a soluble alkaline earth salt. Not only is edge blurring thus no longer a problem, but also, as has been found by experience, it is no longer necessary after washing the treated paper to use the precipitation agent of the aforesaid patent.

The reason why edge blurring is suppressed in this way by the inclusion of a soluble alkaline earth salt in the revivifying solution is not known with certainty. It might be thought that since Prussian blue is a negative lyophobic sol its charge will be neutralized by ions supplying positive charges, and that the elfectiveness of such positive ions would be in the order of the positive charge. In other words, the positive ions of an alkaline earth compound, which carry two positive charges, would be more effective than the alkali metal halide used in the prior practice. However, according to my experience the addition of mono-, diand tri-valent metallic chlorides to solutions made in accordancewith the foregoing patent gives no evidence that increased basicity of the cations gives increased protection against edge blurring. Furthermore, in past practice under the said patent NaCl has been used in such amount that it ispresent in the ratio of 300 or more parts to one part of FeCl;,, where HCl is used as the acid, yet edge blurring occurs. That concentration of sodium ions should be suflicient to precipitate the Prussian blue but it does not so that neutralization of the charge is not alone enough to avoid edge blurring.

Although not confining myself to any particular theory as to the action of the soluble alkaline earth salt, I now believe that it acts to suppress edge blurring by forming a modified Prussian blue in which a portion of the iron is replaced by alkaline earth metal. For instance, it is known that there is a potassium calcium ferrocyanide of the alkali metal of normal sodium or potassium ferrofor most purposes.

cyanide, which in turn reacts with the iron of the ink used in the writing to form a less soluble Prussian blue containing combined alkaline earth in the molecule tests that I have conducted have shown that when Prussian blue is precipitated from solutions used in practicing the method of the foregoing patent to which there has been added a soluble calcium or a soluble barium salt, the precipitate after thorough washing shows a fixation of the alkaline k earth metal. 7 V In the practice of this invention thereis used, as in the past, an aqueous solution of an alkali metal ferrocyanide, such, for example, as sodium or potassium ferrocyanide, although the potassium compound is preferred The exact concentration is not critical, and as little as 0.1 percent by weight maybe used. There is no practical upper limit so that higher concentrations may be used, if desired, although in general that is economically undesirable since low concentrations suffice. For many purposes it is preferred to use about 0.3 percent.

The solution likewise contains an alkali metal halide, suitably potassium or sodium chloride (KCl or NaCl).

The halide. serves chiefly for its mass action effect in forcing the revivifying reaction in the desired direction so that provided enough is present for that action its concentration is not critical. In the case of sodium chloride, about 5 percent by weightsuffices.

The solution contains an acid also, which is believed to function to neutralize any alkalinity of the water used and to solubilize the iron of the writing for reaction to form Prussian blue with the ferrocyanide. The common mineral acids such as hydrochloric (HCl), sulfuric (H 30 nitric (HNOQ, and phosphoric (H PO and others may be used. Organic acids may be used likewise, examples of the latter class being formic (HCOOH), acetic (CH COOH), chloracetic (CH ClCOOI-I), succinic [COOH.(CH .COOH] and others. The amount of; acid present will, obviously, depend upon the particular acid" used, but enough is to be present to neutralize any the iron-will not'be'solubilized. The concentration is, of course,"1'nsufiicient" to injurethe paper; As an example, in the case of hydrochloric acid of customary laboratory strength, the addition of about, 9.2 percent by weight of the acid'sufiicesfor most purposes. l The major feature of the invention is that there is added to :such a solution-atleastone'. soluble salt of calcium or'bariumf Itis preferred tojuse the chlorides (CaCI Bacl although other halides I such as the bromides (CaBr BaBr lor' iodides (Gal Bali) maybe used. Other soluble salts of these alkaline .earth metals may be' used 'likewise fon'lexample'fsuch as the nitrates [Ca(NO Ba(NO )-,;],j .the' thiocyanates- [Ca(SCN) BatSCNhl; the ichl t f T fli loshi t l sh Hereagain the'exact concentration is not critical although formost purposes from about 0.5s percent to as much as 20gpereent by weight may be used. Of course, for economy the lowest effective amount will be used. Althoughthe calcium and barium saltsare preferred, solublefsalts; of strontium (Sr) and, magnesium (Mg) rhaybeusedalthough, according to my experience, they are less satisfactory, in general than the Ca and Ba salts. Althoughmagnesium is commonly considered to be the transition element of groupILyet forthe purposes of this invention it maybe considered tobe an alkaline earth metal. I 2 i i J In the. practice of the invention, .the solution as-just described is made up with water preferably heate'dto 35 to 50 C. to increase the rate of reaction, thepaper carrying thefaded inkwriting isimmerscd in it for a period of time, usually under one minute, to permit thereactions to occur by whichthe written characters are revivified, after which thepaper is withdrawn, washed thoroughly in hot or cold water and then dried. In this way, the brilliance of. the inked characters is restored, edge blurring of the revivified characters is suppressed, and there is no discoloration, at.least to any objectionable extent, of the paperitself. As will be observed, the second precipitation step of the above mentioned patented procedure is unnecessary, and the second washing operation is accordingly eliminated. p v v A further exemplification of the manner in which documents are restored in accordance with the invention: two trays A and B, of impervious material, such as hard rubber, glass or enameled iron, are placed on each side of a water spray, the documentis immersed for 45 seconds in tray A containingf/f570 ml. of water at 45 C., 15ml. of reagent gradeiHCl (,sp. gr. 1.19), 383 gm. of NaCi, 383 gm. of CaOlQZHO, and 24 gm. 'of

K Fe(CN) .3H O; The document is then rinsed momentarily in the water spray, then placed for 45 seconds in tray B containing water at 45 C., and finally squeezed between rubber rolls and dried- The. water spray is not-essential but is preferred.

As another example, the document is placed for 35 seconds in tray A containing 7570 ml. of water at 50. C., 20 ml. of HCl (sp. gr. 1.19), 300gm. of NaCl, 190 gm. of BaCI ZH O, and SOgm. of K Fe(CN) .3H;O, rinsed momentarily in thewaterspray, placed for35 seconds in tray B containing waterat 50 C., squeezed between rubbe r rolls andthen dried. i

,;As indicated above, it is not known whether or not the alkaline earth compound reacts to produce a mixed insoluble ferrocyanide. Howeven'I have found that the inked charactersmay be restored satisfactorily by the use of an aqueous [Ca,Fe(CN) or barium ferrocyanide [Ba Fe(CN) l in concentrations within their solubility ranges in acid, acidified with a mineralacid other than sulfuric, and preferably other than phosphoric also, and that in this solution of calcium ferrocyanide case the presence of an alkali metal salt and of a subsequeiit precipitation step are unnecessary.

may be practiced otherwise than as specifically described.

sodium chloride. 1,

I claim: I

1. In a method" of restoringfaded writings made from iron ink susceptible to-oxidationwith'consequent color fading in which the writingis treated with-an aqueous solution of an alkali metal-ferrocyanide of the group consisting of Na F e(CN and K Fe(CN) containing acid and an alkali-metalhalidefthe improvement consist-.

ing in adding in said solution an ionizable soluble alkaline earth salt.

1 2. -In amethod ofrestoringfaded writings made from iron ink susceptiblegto.oxidation with consequent color fading in which thewriting is treated with an aqueous solution of an alkali metal ferrocyanide of the group consisting of Na Fe(CN) and K Fe(CN) containing acid and an alkali metal halide the improvement consisting in adding in said. solution at least one ionizable salt of a metal of the group consisting ofcalcium'and barium.

3. That method of restoring faded writing on paper made from iron inksusceptible to oxidation with consequent: color fadingcomprisingtreating the paper with an acidified'solutionfinrwater of an alkali metal ferrocyanide of the group consisting of Na Fe(CN) and K Fe( CN),, an alkali metal halide,-and an ionizable alkaline earth metal salt, then washing the paper, and then drying it. w

i 4, A method according to claim 3, said ferrocyanide being potassium ferrocyanide.

5. A method according to claim 4, said halide being 6. A method accordingto claim 5, said solution'being i acidified with hydrochloric acid,

. 'Z. That-method-of restoring faded writing on paper made from ironink susceptible tooxidation with consequent color fading comprising. treating the paper with an acidified solution inywater of an alkalimetal ferro- 9. That method of restoring faded writing on paper made from iron ink susceptible to oxidation with consequent color fadingcompris'ing treating the paper with an acidified solution in water of a substance of the group consisting of calciumferrocyanide and barium ferrocyanide, then washing the paper, and thendrying it.

, 10. A. method according to claim 7 in which the paper is momentarily:subjected to a water spray after removal' from the treating solution and prior to the washing step.

Y ReferencesCited in the file of this patent UNITED STATES PATENTS Schmidt Mar. 11, 1919 Lowy Dec. 5, 1939 However I desire to have it understood that, 

1. IN A METHOD OF RESTORING FADED WRITINGS MADE FROM IRON INK SUSCEPTIBLE TO OXIDATION WITH CONSEQUENT COLOR FADING IN WHICH THE WRITING IS TREATED WITH AN AQUEOUS SOLUTION OF AN ALKALI METAL FERROCYANIDE OF THE GROUP CONSISTING OF NA4FE(CN)6 AND K4FE(CN)6 CONTAINING ACID AND AN ALKALI METAL HALIDE, THE IMPROVEMENT CONSISTING IN ADDING IN SAID SOLUTION AN IONIZABLE SOLUBLE ALKALINE EARTH SALT. 